The present invention relates to a pressure adjustment device, more particularly to a pressure adjustment device, which can adjust the negative pressure inside the ink cartridge timely so as to prevent ink from leaking and prevent inkjet print from not working owing to excess negative pressure.
Drop-on-demand is a generally used method to control ink to output from an ink storage tank to a recording media (such as printing paper) in a conventional inkjet printing. The traditional inkjet pen, which uses drop-on-demand, is generally furnished with hot bubble type or piezoelectric force wave type printing head. The main element of hot bubble type printing head is a thin film resistance, when is heated, a trace of ink drops can be evaporated instantly, fast expansion after evaporation of ink drops cause little ink to pass the injection exit of the printing head again to spray and print onto a printed paper. Although the printing head of drop-on-demand can get ink from the ink storage tank in the inkjet pen effectively to spray ink drops, but drop-on-demand needs a control function to make sure that ink does not leak out of the printing head when the printing head is not working. That such kind of control function stops ink to leak from the printing head is attained by generating a slight negative pressure in the ink storage tank. What is called negative pressure indicates that a part of vacuum is formed in the ink storage tank, it is shown as a positive value as measuring negative pressure, so the increase in negative pressure means the increase of vacuum degree. Ink can be stopped to leak out of the printing head by increasing negative pressure.
Although ink can be stopped to leak out of the printing head by increasing negative pressure, but negative pressure cannot be too large, otherwise it will cause the printing head to be unable to overcome negative pressure and make ink drops to be unable to spray out. Another, the negative pressure in the ink storage tank of the inkjet pen must be able to be adjusted as surrounding pressure changes so as to be kept in an appropriate range. Such as, when the surrounding pressure lowers, the negative pressure for stopping ink to leak out of the printing head is increased relatively. Besides, the xe2x80x9coperation effectxe2x80x9d of the ink storage tank may also affect the negative pressure in the ink storage tank, such as, when the ink in the ink storage tank is consumed continuously; it will cause the negative pressure in the ink storage tank to increase. If the negative pressure is not adjusted appropriately, the printing head is affected gradually by too large negative pressure to change the dimension of the sprayed-out ink drop. It not only influences the printing quality, but also even cannot spray out ink completely at last.
The known pressure adjustment technology, such as the U.S. Pat. Nos. 5,409,134 and 5,505,339 have already revealed an adjuster for adjusting the negative pressure in the ink storage tank. Such kind of adjuster generally is a elastic gasbag the principle it uses is to let the volume of the ink storage tank and the change of the negative pressure be adjusted by the variation of the occupied volume of the elastic gasbag in the ink storage tank. For an example, when surrounding pressure lowers, the negative pressure in the inkjet pen relative to surrounding environment is also lowered. At that time, the adjuster begins to work (the elastic gasbag shrinks) to increase the volume of the ink storage tank so as to increase the negative pressure to prevent ink from leaking. On the contrary, when surrounding pressure arises or the negative pressure in the ink storage tank increases owing to the consumption of ink, this elastic gasbag will expand to lower the negative pressure slightly to prevent ink from leaking. Therefore, such kind of adjuster has an ability of two-ways adjustment of the pressure change.
Although these elastic-gasbag-type adjuster can adjust the negative pressure in the ink storage tank successfully, but in general, the maximum expansion of the elastic gasbag has its own limit, therefore when ink is consumed to a certain extent, the volume of the ink storage tank cannot be changed any more for the reason that the elastic gasbag has already reach the maximum expansion, the result that ink reduces continuously will cause the negative pressure to be too large and to exceed the proper range, therefore, the printing head cannot overcome the negative pressure so that it will cause ink drops to be unable to spray out, and so, ink in the ink storage tank cannot be consumed completely.
Another known pressure adjuster of the inkjet pen is called xe2x80x9cbubble generatorxe2x80x9d, such as the U.S. Pat. Nos. 5,526,030 and 5,600,358. The bubble generator has a nozzle, the ink storage tank communicates with atmosphere via the nozzle. After the dimension of the nozzle is decided appropriately, ink can gather around in the nozzle and constructs a fluid-type seal through capillary force. When the negative pressure is too large, surrounding air will enter into ink storage tank as bubble type, this will cause the negative pressure in the ink storage tank to be lowered. When the negative pressure lowers to a certain extent, the force entering bubble will be smaller than the capillary force so as to rebuild the fluid-type seal to stop bubble to enter no more. However, such kind of pressure adjuster only can adjust pressure variation one way, this is to say, when surrounding pressure lowers, the pressure adjuster will not work, this will cause ink to leak from the nozzle. Besides, the bubble generator control the negative pressure of the ink storage tank through capillary effect between gaps, this will cause that gaps must be controlled precisely, and such kind of the requirement will increase the difficulty of manufacturing and installment. If ink dries at the nozzle, it will cause the pressure adjuster to lose efficacy.
The main object of the present invention is to provide an ink pressure adjustment device for inkjet pen, preventing the negative pressure inside an ink cartridge of an inkjet pen from being too large.
Another object of the present invention is to provide an ink pressure adjustment device for inkjet pen, which doesn""t occupy space, the manufacturing cost thereof is low, the installment thereof is easy and the negative pressure of an ink cartridge can be two-ways adjusted.
The pressure adjustment device reveal a tension valve attached to the surface of the gasbag, this tension valve can operate in coordination with the expansion and shrinkage movements of the gasbag, opens or closes timely an air hole disposed at the surface of the gasbag for communicating atmosphere and the inner part of the ink cartridge by way of the gasbag, particularly before the negative pressure value increase to an extent that the printing head cannot spray out ink, the tension has already open the air hole, part of atmosphere (air) will enter the ink cartridge form the tension valve at that time (probably as a type of bubble), so as to prevent the negative pressure in the ink cartridge from increasing too high to lead to a result that inkjet printing doesn""t work.
In a preferred embodiment of the present invention, the tension valve is made of rubber or other similar materials and is a thin plate element with a slit therein. It is attached on the surface of the gasbag, the curving extent of surface deformation at the gasbag expansion may decide to open or close the tension valve. That the negative pressure in the ink cartridge is higher means the expansion degree of the gasbag increases (it also means that the occupied volume of the gasbag in this ink cartridge increases), the expanding gasbag will open the slit that is attached on the surface of the tension valve owing to the deformation of the surface thereof so as to cause part of atmosphere (air) enter the ink cartridge through this slit to adjust the negative pressure in the ink cartridge.
In another preferred embodiment of the present invention, a tension valve even can replace the spring used in the traditional elastic gasbag, a thin plate type tension valve made of rubber and other similar material is attached on the most parts of the surface of the gasbag, it can provide a proper shrinking force to restrain the expansion of the gasbag through the elasticity of rubber itself and plasticity thereof so as to reduce the occupied volume of the gasbag in the ink cartridge, this is just like the traditional technology to press the gasbag by spring to provide the needed negative pressure.
The detailed description of the present invention and embodiments accompanying the drawings will be described as following.